The continually escalating cost of fuel oil as an energy source and its predicted depletion suggests the use of other type fossil fuels as fuel oil substitutes. The abundance of coal and its ready accessibility presents the need for an immediate direct substitution of coal for fuel oil wherever possible.
Several factors have retarded the immediate substitution of coal for fuel oil. One such factor is the difficulty in transporting the coal in bulk from the point of origin to the place of intended use. Another important factor to be considered in the substitution of coal for fuel oil is the effect of the coal burning by-products on the ecology. The problem of transporting coal over long distances is covered in copending U.S. Pat. Application Ser. No. 595,471 filed July 14, 1975 now abandoned. This copending application entitled "Stable Particulate Suspensions" is incorporated herein by way of reference. The application provides means for forming stable suspensions of finely divided coal dust in water for efficient transport within long distance pipelines. A third factor which is of paramount importance is the necessity of converting oil burning equipment over to the proper facility for burning coal.
In order to reduce the effect of coal burning on the ecology the coal is not directly substituted for fuel oil as an energy source but rather is partially substituted for some of the fuel oil and is burned in combination with the oil. The addition of finely divided coal dust in a combustible organic liquid is shown in U.S. Pat. No. 1,390,228 issued Sept. 6, 1921. This patent discloses the use of approximately 30% finely pulverized coal dust as an adjunct to fuel oil and teaches the addition of lime-rosin grease as a means to keep the finely divided coal dust in suspension within the oil. In order to transport the coal dust-fuel oil mixture through long distance pipelines, mechanical power must be consumed in order to cause the coal dust slurry to become transported within the pipeline and must be applied at intervals to keep the coal dust slurry in motion up to the point of destination.
The purpose of this invention therefore is to provide stable, economical coal dust-fuel oil slurries that have optimum rheological properties in order to provide stable suspensions while maintaining ease-of-pumping and ease-of-burning characteristics.